The present invention relates to shaping glass sheets, and particularly concerns a method and apparatus for shaping a series of glass sheets by the roll forming method. According to the roll forming method, a series of heat-softened glass sheets is conveyed between an upper set and a lower set of forming rolls of complementary shape. When each glass sheet reaches a position between the sets of forming rolls, the latter move relative to one another into a sheet engaging position for sufficient time for the shape of the rolls to be impressed on the glass sheet as the latter passes between the sets of forming rolls. The sets are separated and the shaped glass sheet proceeds to a cooling or quenching station where the glass sheet is cooled to impart either a partial or full temper or an anneal depending on the rate of cooling. When the next heat-softened glass sheet in the series arrives between said sets, the sets are again moved relative to one another to their sheet engaging position. Such continuous sheet movement has resulted in increasing the rate of production of shaped glass sheets.
The need for curved glass sheets has increased tremendously in recent years, particularly with the increase in use of curved glass for windshields, sidelights and rear windows of automobiles. The problem of increasing the rate of production of shaped glass sheets on a mass production line has been recognized and new methods and apparatus that do not necessarily require glass sheets to be stopped at a shaping station have been developed, as is evidenced by U.S. Pat. No. 3,545,951 to Maurice Nedelec and U.S. Pat. No. 3,701,644 to Robert G. Frank. These patents illustrate different embodiments of apparatus for shaping continuously moving glass sheets by the so-called roll forming method.
The Nedelec patented apparatus has capabilities of shaping glass sheets to a limited family of shapes about one axis only to shapes that are of uniform curvature from end to end of the sheets along the path of glass sheet movement through the roll forming apparatus. The Frank patented apparatus is also capable of producing bends about a single axis of bending and in addition can produce compound bends comprising bends about two mutually perpendicular axes or bends whose radii of curvature vary from portion to portion of the bent sheets along the path of sheet movement through the roll forming apparatus. When the Frank patented apparatus has been used to produce simple cylindrical bends about a single axis, from time to time, local deviations in curvature have been discovered. Such deviations from desired curvature are also believed to be inherent in the operation of the Nedelec patented apparatus.
One of the problems associated with roll forming is the development of kinks along one or both longitudinal edges of glass sheets shaped by roll forming apparatus. This is particularly noticeable in the shaping of glass sheets of relatively small dimensions and is termed "edge kinking." Another defect attributed to roll forming that is found in relatively long sheets is excessive sag, particularly in the central portion of the sheet. At times, edge kinking and/or excessive sag was so great that shaped glass sheets fabricated on roll forming apparatus were not acceptable by the customer because of their failure to meet the tolerances established by the customer.
U.S. Pat. No. 3,869,269 to Isaac D. Knapp discloses devices that reduce the deviations from desired shape associated with edge kinking and certain types of excessive sag. The apparatus patented by Knapp makes it possible to reduce the deviations from desired shape by a method which comprises applying additional rolling contact against a portion of one of the surfaces of a newly shaped glass sheet when said portion deviates from the shape desired therefor by at least a predetermined amount before the sheet cools to below its deformation temperature. The additional rolling contact is provided against the upper surface of the glass sheet along its edge in the case edge kinking is present. In case the glass shape produced by roll forming includes too great a sag, the additional rolling contact is applied against the bottom surface only of the glass in its sagged portion to help the glass assume a shape conforming more closely to that desired.
The Knapp invention is designed specifically to produce shaped glass sheets with a minimum of optical defects and free of deviations in shape so great as to be unacceptable in commerce. The apparatus aspect of the Knapp invention involves the incorporation of additional roller means disposed in spaced relation to the conventional forming rolls of roll forming apparatus. Means are provided for supporting said additional roller means in position to engage a portion of the surface of the glass sheet that deviates in the direction of said engaged surface from the shape desired therefor by at least a predetermined amount.
The additional roller means incorporated in the Knapp apparatus is mounted in fixed position. Therefore, it is not flexible in eliminating the problems associated with roll forming as would be desired, particularly, these problems involve excessive sag that is non-uniform along the length of the glass sheets being processed and the shaping of sheets having a pointed end which tend to develop end kinking at the longitudinal extremity of the glass as distinguished from the edge kinking problem solved by the Knapp patent.